Temperature induced phase transition of CaMn_0.5Zr_1.5(PO₄)₃ phosphate

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• 作者：Maria Orlova^a ; ^{maria.p.orlova@gmail.com" class="auth_mail" title="E-mail the corresponding author} ; Lukas Perfler^a ; Martina Tribus^a ; Petr Salnikov^b ; Benoit Glorieux^c ; Albina Orlova^b
• 关键词：Phosphates ; Phase transition ; Crystal structure ; X-ray powder diffraction ; Ab-initio structure solution
• 刊名：Journal of Solid State Chemistry
• 出版年：2016
• 出版时间：March 2016
• 年：2016
• 卷：235
• 期：Complete
• 页码：36-42
• 全文大小：1635 K

文摘

In this work we investigated the structural behaviour of a CaMn_0.5Zr_1.5(PO₄)₃. Due to the presence of divalent Mn²⁺ cations this compound can possess interesting luminescence properties. It was recently understood that this phosphate undergoes a temperature induced irreversible phase transition in the range of 800–875 °C. It has also been shown that the 3d–3d luminescence of Mn²⁺ increases 10 fold for the high temperature polymorph. To determine the Mn environment structural investigations of both phases have been performed by the X-ray powder diffraction and Raman spectroscopy methods. The low temperature modification adopts the trigonal NZP structure type with a slightly lower symmetry (space group R32, a=8.7850(2) Å, c=22.6496(7) Å, V=1514.8(1) Å³). The high temperature form in turn has orthorhombic symmetry (space group Pnma, a=6.2350(3) Å, b=6.6281(3) Å, c=14.4731(6) Å, V=598.13(5) Å³). Both structures were solved ab-initio from powder data and structural analysis was performed. In-situ and RT Raman spectra are consistent with the XRD derived structural model. Mn²⁺ cations occupy different types of positions in these structures and a change in Mn coordination number (6 for LT phase, 7 for HT phase) results in different Mn–O bond lengths. These differences may explain the change in the optical properties between the polymorphs.